Ten Things You Didn’t Know About the Moon

1 The Moon turns once a month

Although it looks as though the Moon doesn’t turn at all, because one side faces Earth all the time, the Moon turns in the same time that it takes to go around the Earth. If you were looking at it from way out in space, you’d see all sides of it as it orbits the Earth every 29½ days. This curious behaviour is called captured rotation, and almost all the other moons in the solar system do the same thing. Captured rotation is caused by the tidal forces between the main body and its moon – they each raise slight tides in the other, even though their materials are solid rock or ice. Over time, these forces result in a slowing of the rotation of the lesser body.

2 There’s a no ‘dark side of the Moon’

At least, there’s no permanent dark side. The dark side is simply the night side, that faces away from the Sun, and this changes all the time, just as on Earth. What people are thinking off when they say ‘the dark side of the Moon’ they really mean its far side – the side facing away from Earth. The light we see from the Moon is just sunlight that’s illuminating it.

3 The Moon was born from Earth

Big Splash (NASA artwork)

The Moon was probably formed early in the formation of the solar system when large objects were careering chaotically around. A body about a third the size of the Earth is thought to have collided with the newly formed Earth, long before it had fully solidified to its present form. The ‘big splash’ that resulted created a ring of material around the Earth that eventually solidified to form the Moon. The Moon’s crust has similar minerals to that of the Earth.

4 Humans owe our existence to the Moon

Many scientists believe that the ocean tides caused by the Moon in the distant past may have aided the spread of life from the oceans to land. The tides create rock pools and intertidal areas where life had the opportunity to evolve to live in a land-based environment. So all land-based animals, including humans, could be the result of our large Moon.

5 The Moon isn’t bigger when it’s close to the horizon

Yes, it certainly looks bigger but this is just an optical illusion. If you measure its size, you’ll find that it’s just as large when it’s high up as when it’s near the horizon. There are lots of competing explanations for the illusion, but it’s probably because we estimate sizes by comparing objects with those in the foreground whose size we know, and the Moon is therefore much bigger than the buildings or trees that we compare it with. But high in the sky there’s little to compare it with.

Photo by moonlight

6 Moonlight isn’t blue

Movies often use blue filters to suggest that an underexposed scene is taking place by moonlight, but moonlight is actually slightly redder than sunlight because of the nature of lunar rocks. Our eyes are not sensitive to colour at low light levels, including even bright moonlight, so we actually see a landscape in shades of grey in the absence of artificial light. Only the sky close to the Moon can look slightly bluish. If you take a photo by moonlight in the countryside, it reveals all the colours that you’d see by daylight.

7 The full Moon doesn’t cause more emergencies

Many people in the emergency services believe this, but there’s no evidence for it. However, the Moon does look almost full for several nights on either side of the actual full Moon date, and the Moon is visible almost all night on these occasions, so there’s a greater chance that a busy night will coincide with what people think is a full Moon than when it’s at any other phase.

8 The full Moon always rises exactly opposite the Sun, and at sunset

The actual full Moon takes place when it’s fully illuminated by the Sun, with virtually no shadows on it at all, and this means that the Sun is opposite the Moon in our sky. So it rises at sunset, and exactly opposite the Sun on the horizon. Lunar eclipses, when the Moon goes through Earth’s shadow, can also take place on the night of exact full Moon. But they don’t take place at every full Moon because the Moon’s orbit is at an angle to the path of the Sun through the sky so it often passes above or below Earth’s shadow. The next lunar eclipse takes place on the early morning of 21 January 2019.

Eclipse timings on 21 January 2019

9 During lunar eclipses, the Moon turns red

Lunar eclipses occur when the Moon passes through Earth’s shadow. But the shadow isn’t completely black, because light from the Sun is transmitted through the atmosphere around the Earth’s rim as seen from the Moon. This light is reddened, as the atmosphere absorbs blue light, just as it does at sunset. So the Moon is bathed in the light from all the world’s sunsets at once. This is why the press refer to an eclipsed Moon as a ‘blood Moon’, and you can view if for yourself on 21 January.

10 Christopher Columbus once used an eclipse of the Moon to save his expedition

In his exploration of the New World, Christopher Columbus stationed himself in Jamaica in 1503. However, after many months the local people became tired of providing him and his crew with food. Columbus had an almanac which predicted a total lunar eclipse on 1 March 1504 and threatened the locals that he would turn the Moon red if they didn’t provide food. Sure enough, the eclipse took place, and the threat worked.